1. Technical Field
Embodiments of the present invention generally relate to an image forming apparatus such as a printer, a facsimile machine, or a copier.
2. Background Art
Various types of electrophotographic image forming apparatuses are known, including copiers, printers, facsimile machines, or multifunction machines having two or more of copying, printing, scanning, facsimile, plotter, and other capabilities. Such image forming apparatuses usually form an image on a recording medium according to image data. Specifically, in such image forming apparatuses, for example, a charger uniformly charges a surface of a photoconductor serving as an image carrier. An optical writer irradiates the surface of the photoconductor thus charged with a light beam to form an electrostatic latent image on the surface of the photoconductor according to the image data. A development device supplies toner to the electrostatic latent image thus formed to render the electrostatic latent image visible as a toner image. The toner image is then transferred onto a recording medium directly, or indirectly via an intermediate transfer belt. Finally, a fixing device applies heat and pressure to the recording medium carrying the toner image to fix the toner image onto the recording medium. Thus, the image is formed on the recording medium.
To stabilize image density of a multi-gradation image formed on a recording medium, such image forming apparatuses typically generate gradation characteristic data using a gradation correction pattern having known gradation levels to correct gradation of image data of a gradation image to be outputted.
For example, a gradation correction pattern having patches for each of a plurality of input gradation levels may be formed on the intermediate transfer belt serving as an image carrier. A density sensor detects image density of each patch. According to the detected density of the gradation correction pattern, gradation characteristic data is generated that shows a relation between the image density and the gradation levels in a gradation range of the multi-gradation image. The gradation is then corrected upon formation of the multi-gradation image using the gradation characteristic data.